Simon Cowell won't return to judge 'The X Factor' in the UK yet because he believes jet-lag ruins his looks.

The 52-year-old music mogul is currently working on the US version of the pop star search show and he won't shoot both series at the same time because he is convinced cross-Atlantic travel ages his face.

A source told The Sun newspaper: "Simon hates the way his face looks when he's jet-lagged and that's the real reason he won't be back.

"When he's tired he gets bags and dark circles under his eyes and he hates that.

"The air-con on the plane also really dries out his skin.

"When he gets off a plane he wears sunglasses to hide his eyes."

Simon is known for his vanity and his lavish beauty regime was recently revealed in a new book, 'Sweet Revenge: The Intimate Life of Simon Cowell', which describes how he has Botox twice a year, intravenous vitamin injections and regular colonic irrigation.

He has said of the latter process, where waste is removed from the bowels by pumping water through a tube into the body: "It's so cleansing - and it makes my eyes shine brighter."

'The X Factor' UK is currently judged by Gary Barlow, Tulisa, Louis Walsh and Nicole Sherzinger. Gary was brought in as head of the panel after Simon left to go to America last year.